Radial piston pumps of the prior art generally comprise at least one radial cylinder, at least one radial piston with associated piston head, at least one piston guide shoe, an eccentric element, and means for attaching the radial piston to the piston guide hose, whereby the piston head with its bearing surface contacts with or without locking or attachment the bearing surface of the associated piston guide shoe or shoes and the piston guide shoe or shoes contacts on its side not pressing on the piston head the eccentric element, and wherein the piston head has an outer shoulder, which is grasped by the device for attaching the radial piston to the piston guide shoe.
According to whether the eccentric element is an eccentric ring or an eccentric shaft, the radial piston is displaced by the eccentric or the cylinder carrier.
It is understood that such a radial piston pump has the usual passages for the guiding and control of liquids, which are not considered a part of the invention and therefore are not described although the references discussed below simply illustrate such means.
The drive or drive stroke can result from motion of the eccentric element or the housing; also the possibility exists to drive these elements with different speeds. (See, for comparison, German Pat. No. DE-PS 11 55 336, column 4, lines 31-51).
In known radial piston pumps of this kind (as taught in German Pat. No. DE-PS 29 15 239) the device for attachment of the radial piston with the piston guide shoe or shoes comprises a connecting ring running around the entire periphery of the radial piston pump, which is radially coupled with both the radial piston and also the eccentric element, whereby the coupling shoes are interconnected and the connecting ring runs concentrically with the motion of the eccentric element.
This may be implemented or performed with reasonable positioning and mounting effort only when the eccentric element is an eccentric ring, as is the case in the embodiments of the prior art. Of course one such connecting ring permits with an eccentric ring the abandonment of a locking attachment between the piston head and the piston guide shoes. However in fast running pumps increased wear and tear in the described structure occurs along the reciprocating path of the eccentric ring. Also one observes distortions in the connecting ring and fatigue fractures.
Inasmuch as the proportions are similar to one other radial piston pump (see, for example, German Pat. No. DE-PS 14 03 748), in which the radial pistons are provided with so clled piston pressure rings, which are positioned on both sides of the radial piston and engage or embrace both sides of the shoulder of the piston head, the drawbacks of the latter system must be considered. Here a locking attachment between the piston body and the piston guide shoes is necessary, which shows premature wear and tear and frequently likewise fatigue fracture.